This disclosure relates generally to a downhole tool used for detecting geological formation properties and, more particularly, to power balancing of the downhole tool.
This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present techniques, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, these statements are to be read in this light and not as admissions of any kind.
To locate and extract resources from a well, a wellbore may be drilled into a geological formation. Downhole tools are placed into the wellbore to identify properties of the downhole environment. For example, a pulsed neutron generator (PNG), which may include a sealed tube, controllable power supplies and high voltage insulation system disposed in a housing, is used, for example, in various types of well logging instruments. The PNG emits bursts of high energy (approximately 14 MeV) neutrons that interact with subsurface formations surrounding a wellbore into which the instrument is inserted. Various types of detectors, e.g., gamma ray detectors, fast neutron detectors, epithermal neutron detectors and thermal neutron detectors may be disposed on the instrument at selected axial distances from the PNG. Numbers of, timing of and/or energy levels of detected neutrons and/or gamma rays may be used to determine selected physical properties of the formations. One example of a PNG tube is described in U.S. Pat. No. 5,293,410 issued to Chen et al., which is incorporated by reference in its entirety.
The PNG may generate a stream of deuterium and tritium (D-T) ions in the neutron generator tube to impact a target. Neutrons are produced from the impact through a nuclear fusion reaction. The PNG may include an ion source having a cathode that emits electrons, which are accelerated toward a grid. Collisions of the electrons with deuterium and tritium may create ions. The PNG may include a filament or reservoir that supplies D-T gas, and an acceleration structure referred to as the accelerator column, in which the ions generated by the ion source may be accelerated by an applied electric field. The high voltage generating the electric field may be generated in a high voltage (HV) power supply. Each of the hardware components of the PNG, such as the filament, the cathode, the grid, the HV power supply, and the like, may draw power at various times from a power system of the PNG, including power supplies for each component. That is, at a given time, some or all of the power supplies may draw different levels of power resulting in unpredictable power surges or decreases in power drawn from the system power supply. For example, at a first point in time, the grid, the cathode, and the filament drive may draw power, and at a second point in time, none of these hardware components may draw power. The system power supply of the downhole tool may have difficulty withstanding variations in power demand of long duration. To address this difficulty, a capacitor bank may be included to smooth energy usage. However, a capacitor bank may be bulky and take up an excessive amount of space in the downhole tool, may increase cost of the PNG, and may include additional circuitry to discharge the capacitor bank and/or to prevent inrush currents, thereby increasing complexity of the PNG.